Robby, let's start with Iodine Dosing first.
IODINE:
Iodine is a mineral nutrient that is naturally present in seawater. These mineral nutrients (such as calcium, selenium, magnesium, potassium, sodium, zinc, and iodine) are chemical elements required by living organisms. Algaes, soft corals, sea sponges, shrimps, shells and fishes can accumulate measurable iodine concentrations, higher than the normal 60 ppb average concentration in the seawater.
Iodine may come from the rocks in your tank, the salt water you mixed up, the fish food you feed your tank, the dried nori seaweed that tangs love to eat, or supplements.
In the ocean, iodine can be found in many different organic and inorganic forms that may change back and forth depending on many factors, pH being one of them. There are two major inorganic forms of iodine species: IODATE ( IO3-) and IODIDE (I-). Organic forms of iodine are formed when they attach to carbon atoms, such as methyl iodide (CH3I).
When iodine is added to water, the following reaction occurs and can move back and forth depending on environmental factors such as pH:
I2(l) + H2O(l) -> IO-(aq) + 2H+(aq) + I-(aq)
But what does all this mean in terms of dosing iodine?? If you dose iodine, it is rapidly being converted to other forms of iodine (called species). These other forms are selectively taken up by algae, corals & fish. It is being absorbed by activated charcoal in a media reactor or sock and probably lost to skimming. Additionally, it is constantly changing its form….as an example, phytoplankton may use iodate, covert it to iodide and release it into the tank.
Because the dosed iodine is readily converted to other forms in the tank water, it is very difficult to measure a TOTAL IODINE concentration. The commercially available hobbyist kits are specific to certain iodine species and can be complex to use. Some kits only detect iodide, iodate and molecular iodine, while others may only detect iodide and molecular iodine.
A better question may be “Do I need to dose iodine?†or “Does dosing Iodine help or hurt the tank?†Since iodine (and its varying forms) seem to be eliminated fairly quickly by skimming, charcoal and algae uptake, supplementation appears to be harmless if kept within reason. As stated above, supplementation can come in the form of feeding the tank fish food, nori, or iodine based chemicals. Overdosing can be harmful, but there is no information available on lethal dose concentrations for varying species of corals, crustaceans and fish.
Anecdotally, I dosed a combination of iodine and iodide for many years in my tank without testing at a rate of 2 mL/100 gallons/week, with a 25 gallon water change every 2 months, active skimming and use of charcoal. I had good coral growth, good crustacean molting, and great macro algae growth. I decided to maintain my tank without iodine supplementation to see if there was any effect. The only detrimental affect I observed was the slower growth of macro algae, but I cannot identify iodine as the cause because I had changed my fuge lighting as well as other modifications. So, I have no opinion on iodine dosing, other than to tell you that the use of available kits for testing may not give you the total concentration. Try it, if it seems to perk up your tank corals and algae, then use it.
I’ll discuss ozonation in my next reply soon. I have to finish remodeling the bathroom first as it is all torn up at this time.
